This page is an official guideline on PvXwiki.
It has wide acceptance among editors and is considered a standard that all users should follow.
The style and formatting at PvXwiki is often complex, or at least, unobvious. If you don't know where or how to add something, add it anyway! It will be moved and adjusted by other editors to better fit within the context of the page.
Unfortunately, the articles meant to house standards for style and formatting are currently way out of date. Hopefully, somebody will take up the sword and clean these up.
Along the same lines, please don't add unnecessary style information to the pages. Creating a nice infobox to float on the right side of an article is fine—they're extremely useful, and contained within a template. However, adding divs to move the table of contents, or color a section differently, or cause any behavior that makes an article inconsistent with the rest of the wiki is usually a bad idea. There a few indexes on the wiki which have very different formatting than the rest of the articles—the Main Page itself is a good example—but in general, all the pages look pretty much the same. This is good for our users (continuity makes access easier) and good for our editors (less arcane syntax and formatting makes adding or editing content much easier).